The present invention relates generally to a semiconductor memory apparatus, and more particularly, to the data input and output of a semiconductor memory apparatus.
Typically, in a semiconductor memory apparatus, the number of inputs and outputs varies depending upon an input and output mode. The input and output mode indicates the number of data which may be inputted and outputted by the semiconductor memory apparatus at a time. X4, X8 and X16 designate input and output modes. X4 means that a semiconductor memory apparatus may input and output four data at a time, X8 means that a semiconductor memory apparatus may input and output eight data at a time, and X16 means that a semiconductor memory apparatus may input and output sixteen data at a time. X4 and X8 are preferably adopted for servers and desktop computers, and X16 is preferably adopted for graphic applications and notebook computers.
Data transmission of semiconductor memory apparatuses is divided into single-ended signal transmission and differential signal transmission. The single-ended signal transmission has the number of channels for data transmission to be less than that of the differential signal transmission. That is, the semiconductor memory apparatuses adopted for the single-ended signal transmission may accomplish a high transmission rate from being able to use a decreased number of channels.
However, when the single-ended signal transmission is adopted, disadvantages occur, wherein a substantial amount of noise is generated. Also, and the increase of a data transmission rate greater than a predetermined level becomes difficult, because the bandwidth of the channels are typically limited by design.
To overcome the above problems generated by the single-ended signal transmission, the differential signal transmission is adopted. The differential signal transmission has its own problems caused by increasing the number of channels for data transmission. For example, when the number of differential signal transmission has twice as many transmission channels as the single-ended signal transmission the number of pads required are double for a chip. Therefore, the doubling of the pads causes the area of a semiconductor memory apparatus to increase. This increase of area on the chip from the increase pads does not accommodate the trend toward miniaturization of a semiconductor memory apparatus.